In an EGR system, an EGR passage is provided between an exhaust passage and an intake passage, and a part of exhaust gas is recirculated to the intake side via the EGR passage. For example, Patent Document 1 introduces a valve assembly for adjusting the flow amount of exhaust gas to be recirculated.
FIG. 9 shows an axial sectional view of a valve assembly described in Patent Document 1. As shown in FIG. 9, a valve assembly 100 is disposed between an exhaust manifold 101 and an intake manifold 102.
The valve assembly 100 includes a housing 103, a butterfly valve 104, bearings 105a and 105b, and wire filters 106a and 106b. The housing 103 is formed of stainless steel (SUS). A stem 104a of the butterfly valve 104 is inserted to a stem hole 103a of the housing 103.
FIG. 10 shows an enlarged view of the inside a frame X of FIG. 9. As shown in FIG. 10, the wire filter 106a is disposed between the inner circumferential surface of the stem hole 103a and the outer circumferential surface of the stem 104a. The wire filter 106a is formed of fibers of stainless steel (not shown) intertwined in mesh form. With the wire filter 106a, dust such as soot in the exhaust gas flowing through a gas passage 107 can be collected. Therefore, the bearing 105a can be protected from the dust.    [Patent Document 1] Japanese Patent Application Publication No. JP-A-2007-32301    [Patent Document 2] Japanese Patent Application Publication No. JP-A-2005-256803